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improve lod tile loading for projections #11225

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merged 2 commits into from Nov 5, 2021
Merged

improve lod tile loading for projections #11225

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d804604
improve lod tile loading for projections
ansis Nov 4, 2021
826d3c1
fixup
ansis Nov 4, 2021
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17 changes: 10 additions & 7 deletions src/geo/projection/adjustments.js
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Expand Up @@ -8,21 +8,24 @@ import type {Projection} from './index.js';
import type Transform from '../transform.js';

export default function getProjectionAdjustments(transform: Transform, withoutRotation?: boolean) {
const projection = transform.projection;

const interpT = getInterpolationT(transform);

const zoomAdjustment = getZoomAdjustment(projection, transform.center);
const zoomAdjustmentOrigin = getZoomAdjustment(projection, LngLat.convert(projection.center));
const scaleAdjustment = Math.pow(2, zoomAdjustment * interpT + (1 - interpT) * zoomAdjustmentOrigin);

const matrix = getShearAdjustment(transform.projection, transform.zoom, transform.center, interpT, withoutRotation);

const scaleAdjustment = getScaleAdjustment(transform);
mat4.scale(matrix, matrix, [scaleAdjustment, scaleAdjustment, 1]);

return matrix;
}

export function getScaleAdjustment(transform: Transform) {
const projection = transform.projection;
const interpT = getInterpolationT(transform);
const zoomAdjustment = getZoomAdjustment(projection, transform.center);
const zoomAdjustmentOrigin = getZoomAdjustment(projection, LngLat.convert(projection.center));
const scaleAdjustment = Math.pow(2, zoomAdjustment * interpT + (1 - interpT) * zoomAdjustmentOrigin);
return scaleAdjustment;
}

export function getProjectionAdjustmentInverted(transform: Transform) {
const m = getProjectionAdjustments(transform, true);
return mat2.invert([], [
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19 changes: 9 additions & 10 deletions src/geo/transform.js
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Expand Up @@ -14,7 +14,7 @@ import {Aabb, Frustum, Ray} from '../util/primitives.js';
import EdgeInsets from './edge_insets.js';
import {FreeCamera, FreeCameraOptions, orientationFromFrame} from '../ui/free_camera.js';
import assert from 'assert';
import getProjectionAdjustments, {getProjectionAdjustmentInverted} from './projection/adjustments.js';
import getProjectionAdjustments, {getProjectionAdjustmentInverted, getScaleAdjustment} from './projection/adjustments.js';
import {getPixelsToTileUnitsMatrix} from '../source/pixels_to_tile_units.js';

import {UnwrappedTileID, OverscaledTileID, CanonicalTileID} from '../source/tile_id.js';
Expand Down Expand Up @@ -720,7 +720,9 @@ class Transform {
const maxRange = options.isTerrainDEM && this._elevation ? this._elevation.exaggeration() * 10000 : this._centerAltitude;
const minRange = options.isTerrainDEM ? -maxRange : this._elevation ? this._elevation.getMinElevationBelowMSL() : 0;

const sizeAtMercatorCoord = mc => {
const scaleAdjustment = getScaleAdjustment(this);

const relativeScaleAtMercatorCoord = mc => {
// Calculate how scale compares between projected coordinates and mercator coordinates.
// Returns a length. The units don't matter since the result is only
// used in a ratio with other values returned by this function.
Expand All @@ -744,11 +746,9 @@ class Transform {

// Calculate the size of a projected square that would have the
// same area as the reprojected square.
return Math.sqrt(dx * dy) / offset;
return Math.sqrt(dx * dy) * scaleAdjustment / offset;
};

const centerSize = sizeAtMercatorCoord(MercatorCoordinate.fromLngLat(this.center));

const aabbForTile = (z, x, y, wrap, min, max) => {
const tt = tileTransform({z, x, y}, this.projection);
const tx = tt.x / tt.scale;
Expand Down Expand Up @@ -850,21 +850,20 @@ class Transform {
dzSqr = square(it.aabb.distanceZ(cameraPoint) * meterToTile);
}

let scaleAdjustment = 1;
let tileScaleAdjustment = 1;
if (!isMercator && actualZ <= 5) {
// In other projections, not all tiles are the same size.
// Account for the tile size difference by adjusting the distToSplit.
// Adjust by the ratio of the area at the tile center to the area at the map center.
// Adjustments are only needed at lower zooms where tiles are not similarly sized.
const numTiles = Math.pow(2, it.zoom);
const tileCenterSize = sizeAtMercatorCoord(new MercatorCoordinate((it.x + 0.5) / numTiles, (it.y + 0.5) / numTiles));
const areaRatio = tileCenterSize / centerSize;
const relativeScale = relativeScaleAtMercatorCoord(new MercatorCoordinate((it.x + 0.5) / numTiles, (it.y + 0.5) / numTiles));
// Fudge the ratio slightly so that all tiles near the center have the same zoom level.
scaleAdjustment = areaRatio > 0.85 ? 1 : areaRatio;
tileScaleAdjustment = relativeScale > 0.85 ? 1 : relativeScale;
}

const distanceSqr = dx * dx + dy * dy + dzSqr;
const distToSplit = (1 << maxZoom - it.zoom) * zoomSplitDistance * scaleAdjustment;
const distToSplit = (1 << maxZoom - it.zoom) * zoomSplitDistance * tileScaleAdjustment;
const distToSplitSqr = square(distToSplit * distToSplitScale(Math.max(dzSqr, cameraHeightSqr), distanceSqr));

return distanceSqr < distToSplitSqr;
Expand Down